The term "separator for an electrolytic capacitor" is commonly used to designate a storage member containing liquid electrolyte that constantly impregnates both of the capacitor electrodes (the anode and the cathode). The invention is particularly applicable to electrolytic capacitors used at operating voltages of more than 100 volts DC. The invention is equally applicable to electrolytic capacitors used at any voltage with alternating current, sinusoidal or otherwise.
Conventional separators in use nowadays for manufacturing electrolytic capacitors are generally made of one or more sheets of paper or films of paper. These sheets of paper are of different thicknesses and/or densities depending on which final characteristics are of most concern. The general procedure used for defining the thickness and the density of the various sheets of paper used is as follows.
For a capacitor in which lifetime is of major concern, the separator is made from a plurality of thick sheets. The space available between the electrodes is at a maximum, thereby enabling it to contain a maximum amount of electrolyte; however this penalizes physical dimensions which become very large.
For a capacitor in which the major concern is low series resistance, the separator is made of a small number of low-density sheets. The "visibility" between the electrodes is then at a maximum, but this is particularly to the detriment of lifetime due to lack of electrolyte and/or to electric arcs being struck.
For a capacitor in which the major concern is small physical dimensions, the separator is thin and dense, to the detriment of its series resistance and of its lifetime.
It will be understood from reading the above that although the separators on offer heretofore enable an important parameter to be enhanced, this is generally to the detriment of other parameters that are not negligible.
Other solutions that are slightly different from the above-specified situations have also been proposed.
Thus, for example, proposals have been made for so-called "duplex" papers made up of various identical layers of cellulose.
Papers have also been proposed made up of a mixture of cellulose fibers and of synthetic fibers in a single-layer mass. Such papers have the particular advantage of lowering series resistance.
Other substitutions have also been attempted, by including various fillers in the paper, by assembling the paper with a film having microperforations, by impregnating the paper, or by adding a film thereto. Nevertheless, such substitutions have not so far replaced the usual separators as described above.
Accompanying FIG. 1 is a diagram showing a first type of commonly-used separator. FIG. 1 shows a separator 10 placed between an anode 1 and a cathode 2. The separator 10 comprises three sheets of paper 11, 12, and 13, and more precisely three sheets of paper 11, 12, and 13 each having a thickness of 50 .mu.m and a relative density of 0.45.
A second type of separator in common use is shown diagrammatically in FIG. 2. FIG. 2 shows a separator 20 placed between an anode 1 and a cathode 2. The separator 20 comprises three superposed sheets of paper 21, 22, and 23, and more precisely two sheets 21 and 22 of thickness 50 .mu.m and of relative density 0.3, and one sheet of paper 23 of thickness 20 .mu.m and of relative density 0.8.
Overall, the separators proposed in the past have given good service. However they do not give full satisfaction.
An object of the present invention is to provide a novel separator for an electrolytic capacitor enabling electrolytic capacitors to be made which are suitable for operating under high voltage, while nevertheless improving the characteristics of the capacitor, in particular with respect to its physical dimensions, its lifetime, and its series resistance.